The present invention relates generally to integrated circuit memory devices, and more specifically to column redundancy circuitry of integrated circuit memory devices.
Random defects of a manufacturing process used to produce integrated circuit memory devices can render non-redundant elements of an integrated circuit memory device, such as columns and rows, defective. The random defects associated with a manufacturing process may be caused by a number of factors, including particle defects such as broken or shorted out columns and rows, particle contamination, bit defects, locked rows and locked columns.
Redundant elements of a integrated circuit memory devices, such as redundant rows and redundant columns, are used to compensate for these random process defects. During initial testing of an integrated circuit memory device, defective elements are replaced by non-defective elements referred to as redundant elements. Thus, redundant columns and redundant rows are used to replace defective prime columns and rows, respectively, discovered during initial testing of the integrated circuit memory device. The use of redundant elements are extremely important, then, in increasing the overall yield of an integrated circuit memory device.
With ever increasing densities and smaller feature sizes in integrated circuit memory devices, cell redundancy has become more and more important to the proper functioning of larger memory devices. Most memories now require both row and column redundancy. Typical column redundancy schemes provide flexibility but often have the disadvantage of a large programming overhead. Programming overhead refers to the circuitry required to substitute a functional
redundant element for a defective non-redundant or prime element, such as replacing a defective prime column with a redundant column. Circuitry which typically contributes to programming overhead of a column redundancy scheme includes block select programming circuitry and word line driver circuitry. Block select programming circuitry determines which block of a multiple block integrated circuit memory device will be selected to have a defective non-redundant element replaced with a functional redundant element. Word line driver circuitry is typically required for both redundant columns as well as regular or prime columns and this, of course, further swells the size of local wordline driver overhead associated with column redundancy for an integrated circuit memory device. Thus, it would be desirable to provide flexible column redundancy without a large programming overhead.